Type: Package
Title: Acoustic Scattering for Complex Shapes by Using the DWBA
Version: 0.1.1
Date: 2024-01-01
Author: Juan Domingo Gonzalez [cre, aut], Edmundo Federico Lavia [aut], Guadalupe Cascallares [aut]
Maintainer: Juan Domingo Gonzalez <juanrst@hotmail.com>
Description: Uses the Distorted Wave Born Approximation (DWBA) to compute the acoustic backward scattering, the geometry of the object is formed by a volumetric mesh, composed of tetrahedrons. This computation is done efficiently through an analytical 3D integration that allows for a solution which is expressed in terms of elementary functions for each tetrahedron. It is important to note that this method is only valid for objects whose acoustic properties, such as density and sound speed, do not vary significantly compared to the surrounding medium. (See Lavia, Cascallares and Gonzalez, J. D. (2023). TetraScatt model: Born approximation for the estimation of acoustic dispersion of fluid-like objects of arbitrary geometries. arXiv preprint <doi:10.48550/arXiv.2312.16721>).
Encoding: UTF-8
License: GPL-2 | GPL-3 [expanded from: GPL (≥ 2)]
Imports: Rcpp (≥ 1.0.9)
LinkingTo: Rcpp, RcppArmadillo
RoxygenNote: 7.2.3
NeedsCompilation: yes
Packaged: 2024-01-29 22:36:15 UTC; juan
Repository: CRAN
Date/Publication: 2024-01-29 23:20:02 UTC

read_mesh

Description

This function reads the mesh from a file .mesh (extension)

Usage

read_mesh(meshfile)

Arguments

meshfile

a string with the name of the file that contains the volumetric mesh in GMF format (Gamma Mesh Format), conventionally, an ASCII file with ".mesh" extension.

Value

a list representing the mesh, it should include

Examples




# Generates a pseudofile that has  the mesh of
# a cube with edges one metre in length, centered at the origin.

pseudofile=c("MeshVersionFormatted 2",
  "","Dimension 3","","Vertices","8","-0.5 -0.5 0.5 6 ",
   "-0.5 -0.5 -0.5 7 ","-0.5 0.5 0.5 9 ","-0.5 0.5 -0.5 11 ",
   "0.5 -0.5 0.5 16 ","0.5 -0.5 -0.5 17 ","0.5 0.5 0.5 19 ",
   "0.5 0.5 -0.5 21 ","","Edges", "12","2 1 5 ","1 3 8 ",
   "4 3 10 ","2 4 12 ","6 5 15 ","5 7 18 ","8 7 20 ","6 8 22 ",
  "2 6 25 ","1 5 26 ","4 8 29 ","3 7 30 ","","Triangles",
  "12","2 1 3 3 ","3 4 2 3 ","5 6 8 13 ","8 7 5 13 ",
  "2 6 5 23 ","5 1 2 23 ","8 4 3 27 ","3 7 8 27 ","2 4 8 31 ",
  "8 6 2 31 ","3 1 5 33 ","5 7 3 33 ","","Tetrahedra",
  "5","5 2 1 3 1 ","4 2 8 3 1 ","8 5 7 3 1 ","8 2 6 5 1 ",
  "3 2 8 5 1 ","","End","" )

# creating an empty temporary mesh file
temp_mesh_file=tempfile(fileext = ".mesh")
# loading the file with data.
writeLines(pseudofile,temp_mesh_file)
# reading the mesh
my_mesh=read_mesh( meshfile=temp_mesh_file)

# see the bounding box of the volumetric mesh.
lapply(my_mesh$vertex,range)

# unliking the teporary file.
unlink(temp_mesh_file)

tetrascatt

Description

This function computes the volumetric backscattering from a mesh of tetrahedrons.

Usage

tetrascatt(parameters, freq, mesh, kversor)

Arguments

parameters

a list including the parameters model, it must include

  • cw: sound speed in the water in m/s

  • g: g density constrast value, i.e g= rho1/rhow, where rho1 and rhow are the density values of the stcatterer and the media (sea water) respectively.

  • h: h density sound speed contrast value, that is h= c1/cw where c1 is the sound speed of the stcatterer.

freq

an array of frequencies where the scattering is computed.

mesh

a list representing the mesh, it must include

  • vertex: a data.frame with the vertex of the tetrahedra, each vertex has to have three coordinates.

  • tetra: a data.frame containing the four index of each tetrahedra.

kversor

A three component vector that indicates the direction of the incident plane wave.

Value

List containing the frequencies, freq, and their corresponding Target Strength values, ts .

See Also

read_mesh to get this kind of list from a .mesh file.

Examples



#########################################
### Set  the Frequency range    ########
#########################################
fmin=12
fmax=400
freqs= seq(fmin,fmax, by=1)
# for tetrascatt freq unities  should be in Hz.
freq=freqs*1000
############################################################
########### Set properties of media and scatterer ######
############################################################
cw <- 1477.4 #soundspeed surrounding fluid (m/s)
rho <- 1026.8 #density surrounding fluid (kg/m^3)
g <- 1028.9/rho #density contrast
h <- 1480.3/cw #soundspeed contrast
my_parameters=list(cw=cw,g=g,h=h)

##########################################################
### Set the incident direction of the plane wave #####
##########################################################
kversor=c(1,0,0)

##########################################################
### Set the scatterer geometry #######################
##########################################################
# generates a pseudofile that has  the mesh of cube of one meter
# side
pseudofile=c("MeshVersionFormatted 2",
  "","Dimension 3","","Vertices","8","-0.5 -0.5 0.5 6 ",
   "-0.5 -0.5 -0.5 7 ","-0.5 0.5 0.5 9 ","-0.5 0.5 -0.5 11 ",
   "0.5 -0.5 0.5 16 ","0.5 -0.5 -0.5 17 ","0.5 0.5 0.5 19 ",
   "0.5 0.5 -0.5 21 ","","Edges", "12","2 1 5 ","1 3 8 ",
   "4 3 10 ","2 4 12 ","6 5 15 ","5 7 18 ","8 7 20 ","6 8 22 ",
  "2 6 25 ","1 5 26 ","4 8 29 ","3 7 30 ","","Triangles",
  "12","2 1 3 3 ","3 4 2 3 ","5 6 8 13 ","8 7 5 13 ",
  "2 6 5 23 ","5 1 2 23 ","8 4 3 27 ","3 7 8 27 ","2 4 8 31 ",
  "8 6 2 31 ","3 1 5 33 ","5 7 3 33 ","","Tetrahedra",
  "5","5 2 1 3 1 ","4 2 8 3 1 ","8 5 7 3 1 ","8 2 6 5 1 ",
  "3 2 8 5 1 ","","End","" )

# creating an empty temporary mesh file
temp_mesh_file=tempfile(fileext = ".mesh")
# loading the file with data.
writeLines(pseudofile,temp_mesh_file)


#reading the mesh
my_mesh=read_mesh( meshfile=temp_mesh_file)

# Computing the scattering
output= tetrascatt(parameters=my_parameters,freq,
                   mesh=my_mesh,kversor)

plot(output$freq,output$ts)

# unliking the teporary file.
unlink(temp_mesh_file)

tetrascatt_c

Description

Computes scattering from a volumetric mesh efficientlty, it is an auxiliary function called by tetrascatt function.

Usage

tetrascatt_c(cw, g, h, freq, Tet, Ver, kversor)

Arguments

cw

sound speed in the water in m/s

g

density constrast value, i.e g= rho1/rhow, where rho1 and rhow are the density values of the stcatterer and the unbounded medium respectively

h

density sound speed constrast value i.e h= c1/cw, where c1 is the sound speed of the stcatterer

freq

an array of frequencies, where the scattering is computed.

Tet

a matrix containing the four index of each tetrahedron.

Ver

a matrix with the vertex of the tetrahedra, each vertex has to have three coordinates.

kversor

three component vector that indicates the direction of the incident plane wave.

Value

A complex number array which contains the backward differential far-field scattering cross-section (f infinity) values at each frequency.

See Also

tetrascatt